Sorry but it's very simple. Look at the Bluetooth "Profiles" and you don't find a multicast audio system.
http://en.wikipedia.org/wiki/Bluetooth_protocols and the demo of such was just that. Never made it into the spec.
This means you need 2 transmitters and 2 headsets.
I am looking for a cheap (under 40 bucks) bluetooth reciever or headset that can pair with two devices. Can anyone help me on this, or do bt recievers only have the ability to pair w/ one device?